What’s Ailing Your Stream? CADDIS Can Help You Find Out

EPA researchers have updated an online tool that helps scientists from states and tribes find out what’s harming plant and animal life in streams, rivers, and wetlands.

Something was amiss in Long Creek. Biologists from the state of Maine noticed that organisms that should live in the creek were being replaced by ones known to withstand pollution. But what was causing the change? Increased storm flow from new parking lots? De-icing chemicals from roads and the airport? Nutrients and pesticides from the golf course? The scientists were interested in improving Long Creek—but to develop an effective management plan, they needed to know what to fix.

An EPA tool called CADDIS helped biologists from the state of Maine and their EPA collaborators figure it out.

CADDIS, or the Causal Analysis/Diagnosis Decision Information System, is an application that uses EPA’s Stressor Identification (SI) process, supporting information, and other assessment tools to help scientists systematically evaluate the causes of harm to plants and animals in aquatic habitats.

CADDIS helps environmental scientists systematically determine why a body of water is biologically impaired. In some instances, the process produces a clear-cut answer. In other cases, it points to several possible explanations and suggests additional tests that can narrow down the possibilities.

Scientists sample the insects and other tiny creatures that live in a body of water as one way of evaluating its health. The kinds of creatures that live in healthy environments are different from those that live in troubled areas, so these counts serve as an indicator of whether or not all is well.

The name CADDIS is not only an acronym; it also refers to caddisflies, a group of insects used by biologists to monitor stream health.

At Long Creek, the composition of the community of macroinvertebrates was not the only indication that the creek was in trouble. The brook trout population that had historically inhabited the stream had vanished. Maine state biologists and EPA scientists used the SI process described on CADDIS website to help them analyze the problems in the creek and identify their possible causes.

As EPA ecologist Kate Schofield explains, they found not one probable cause but several—and all were related to urban development. Multiple effects of urbanization—such as altered water flow, decreased amounts of dissolved oxygen in the water, and the presence of toxic substances—were interacting to harm the animal life in Long Creek.

CADDIS has helped solve environmental mysteries in many areas of the country, including the Willimantic River in Connecticut, the Little Scioto River in Ohio, the Touchet River in Washington state, and the Bogue Homo River in Mississippi. At least 15 states have used either CADDIS or EPA’s SI process.

A new, enhanced version of CADDIS was released in September 2010. “An important feature added for the 2010 release,” explains Schofield, “is new modules on five topics: physical habitat, pH, insecticides, herbicides, and ammonia.” These new modules, added to the eight preexisting modules on other stressors such as flow alteration, temperature, and sediment, have broadened the variety of situations that CADDIS can help scientists to address.

“The new CADDIS also includes a module on urbanization,” Schofield says. “This module takes a different approach, by focusing on a source of impairment rather than a specific stressor. It provides background information on urbanization in streams and the kinds of issues you need to think about if you suspect that urban development is significantly affecting your stream.”

“Another new section of CADDIS provides case studies that walk users through the assessments that different states have done,” adds Schofield. The case studies come from several parts of the country and focus on different types of habitats. The 2010 release also includes an interactive tool for building conceptual diagrams and linking these diagrams to evidence published by other researchers.

CADDIS helps state agencies improve the condition of streams and other bodies of water by helping them pinpoint the causes of problems so that remedial actions can be targeted where they will do the most good. By providing expanded guidance and resources, the 2010 release of CADDIS will enable watershed managers to better protect the health of our Nation’s waters.